Field of the Invention
The present invention relates to a magnetoelastic sensor and, more specifically, to a magnetoelastic sensor for sensing tension or compression.
Description of Related Art
Conventional tension and compression sensors use strain gauges to produce electrical signals which indicate the tension or compression present. Illustrated in FIG. 13 is a conventional strain gauge, generally designated as 1300. The strain gauge 1300 comprises an input 1310 and an output 1320 connected by a plurality of windings 1330. The input 1310, output 1320, and plurality of windings 1330 are formed from a thin-film conductor 1340, such as a metal foil. The input 1310, output 1320, and plurality of windings 1330 are disposed on an insulative substrate 1350.
The insulative substrate 1350 is adhered to a surface for which strain is desired to be measured. Strain is measured by sensing a resistance of the thin-film conductor 1340 as the strain gauge 1300 is deformed when under tension or compression. When stretched in a direction indicated by A or B in FIG. 13, the resistance of the thin-film conductor 1340 increases. Thus, by measuring the increase in resistance, the tension of the surface to which the strain gauge 1300 is attached may be inferred. When compressed in a direction opposite to that indicated by A or B in FIG. 13, the resistance of the thin-film conductor 1340 decreases. Thus, by measuring the decrease in resistance, the compression of the surface to which the strain gauge 1300 is attached may be inferred.
S-shaped tension or compression sensors, also known as load cells, typically incorporate one or more conventional strain gauges 1300 to sense tension or compression. Illustrated in FIG. 14 is a conventional S-shaped load cell, generally designated as 1400. The load cell 1400 comprises a first arm 1410, a second arm 1420, and a body 1430. Disposed on the body is a plurality of strain gauges 1440A through 1440D. Each strain gauge 1440 may be a strain gauge 1300.
The load cell 1400 detects an amount of force applied in directions generally designed as C in FIG. 14. When the force is applied in the directions C, the strain gauges 1440A and 1440D undergo compression, and the strain gauges 1440B and 1440D undergo tension. By measuring the tension and compression, the size of the force can be calculated.
Conventional tension sensors using magnetoelastic effects are described in U.S. Pat. Nos. 5,195,377 to Garshelis, and U.S. Pat. No. 6,220,105 to Cripe. A conventional Villari effect tension sensor is described in U.S. Pat. No. 5,905,210 to O'Boyle et al.